1. Field of the Invention
This invention pertains generally to a unique catalyst and associated catalytic processes that operate at low pressures, for the direct, efficient production of high quality diesel-type fuels. These diesel-type fuels have a high cetane number, good lubricity, and almost no sulfur which are ideal as either a neat fuel, as a blend with current diesel-type fuel stocks for use in light and heavy duty diesel vehicles, as aviation fuels, in off-road diesel vehicles, in emerging gasoline direct injection engines, and in other applications.
More particularly, the present invention pertains to catalytic processes that allow for the elimination of costly and complex hydrocracking or other product upgrading steps, commonly employed in traditional Fischer Tropsch (F-T) processes, thus enabling the economical production of diesel fuel or diesel fuel blending stocks from distributed production plants that typically produce less than 100 million gallons per year of fuel, although much larger plants can use these processes. Examples of such distributed production plants include biomass or biogas to diesel fuel production plants, stranded natural gas to diesel fuel production plants, carbon dioxide to diesel fuel production plants, and other remote or mobile applications.
2. Description of Related Art
Global demand for energy continues to rise at a significant rate, particularly among developing industrialized nations. Natural gas, biomass, and other alternative resources, such as stranded natural gas, are becoming more attractive as energy sources due to increasing energy costs as well as for environmental reasons.
It is known in the art that biomass can be converted into syngas from a variety of known thermochemical conversion methods, including gasification and other methods. Coal or other carbonaceous solids can also be converted to syngas using gasification and other methods. Natural gas, carbon dioxide, biogas and other gases can also be converted into syngas using a variety of known reforming methods including steam methane reforming, dry reforming, autothermal reforming, and other methods that are known in the art. Technologies for the production of syngas from other carbonaceous resources are also widely known and emerging processes are also under development.
The catalytic hydrogenation of carbon monoxide to produce light gases, liquids and waxes, ranging from methane to heavy hydrocarbons (C80 and higher) in addition to oxygenated hydrocarbons, is typically referred to Fischer-Tropsch (or F-T) synthesis. Traditional F-T processes primarily produce a high weight (or wt. %) F-T wax (C25 and higher) from the catalytic conversion process. These F-T waxes are then hydrocracked and/or further processed to produce diesel, naphtha, and other fractions. During this hydrocracking process, light hydrocarbons are also produced, which may require additional upgrading to produce viable products. Some of these processes are known and described in the art.
For example, U.S. Pat. No. 6,262,131 B1 (Syntroleum), issued Jul. 17, 2001, describes a structured Fischer-Tropsch catalyst system and method that includes at least one structure having a catalytic surface, such catalytic surface having a linear dimension exceeding 20 mm, a void ratio exceeding 0.6, and a contour that causes non-Taylor flow when CO and H2 pass through the structure. F-T catalysts, including iron and cobalt, are described in the patent.
U.S. Pat. No. 4,499,209 (Shell Oil Company), issued Feb. 12, 1985, describes a Fischer-Tropsch catalyst prepared by impregnation of a silica carrier with a solution of zirconium and titanium, followed by calcination and other preparation steps.
U.S. Pat. No. 5,620,670 (Rentech, Inc.), issued Apr. 15, 1997, describes a catalytic process converting hydrogen and carbon monoxide in a Fischer-Tropsch synthesis reactor using a promoted iron oxide catalyst slurry.
These patents describe catalysts that form high hydrocarbon reaction products (e.g., wax) that require further processing, including hydro-processing and other upgrading processes, to produce diesel fuel or diesel blendstock (C8-C24).
Hydrocracking and other upgrading processes add significant expense and complexity to a plant design. Such processes can be justified for large, refinery scale plants. However for smaller, distributed applications such as biomass-to-liquids (BTL), gas-to-liquids (GTL), and other plants that produce less than 100 million gallons of fuel per year, plant designs that incorporate traditional F-T processes that include hydrocracking and other expensive upgrading processes may not be economically viable.
To date, F-T type catalyst and catalytic process plant designs have not been available to support these smaller, distributed applications that allow for the direct production of diesel type fuels.
Accordingly, there is an increasing need for a catalytic process that can directly convert syngas into a diesel fuel with a high yield at relatively low cost under mild operating conditions. There is also a need for a catalytic process that does not require traditional hydrocracking and upgrading steps, thus enabling the economic production of BTL, GTL, and other types of plants that produce less than 100 million gallons of product per year. The present invention meets these needs as well as others and provides a substantial improvement over the prior art.